linux-kernel - [PATCH 05/27] blk-iocost: clamp inuse and skip noops in __propagate

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Date:   Tue,  1 Sep 2020 14:52:35 -0400
From:   Tejun Heo <tj@...nel.org>
To:     axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, newella@...com,
        Tejun Heo <tj@...nel.org>
Subject: [PATCH 05/27] blk-iocost: clamp inuse and skip noops in __propagate_weights()

__propagate_weights() currently expects the callers to clamp inuse within
[1, active], which is needlessly fragile. The inuse adjustment logic is
going to be revamped, in preparation, let's make __propagate_weights() clamp
inuse on entry.

Also, make it avoid weight updates altogether if neither active or inuse is
changed.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 block/blk-iocost.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 78e6919153d8..8dfe73dde2a8 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -897,7 +897,10 @@ static void __propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse)
 
 	lockdep_assert_held(&ioc->lock);
 
-	inuse = min(active, inuse);
+	inuse = clamp_t(u32, inuse, 1, active);
+
+	if (active == iocg->active && inuse == iocg->inuse)
+		return;
 
 	for (lvl = iocg->level - 1; lvl >= 0; lvl--) {
 		struct ioc_gq *parent = iocg->ancestors[lvl];
-- 
2.26.2